1. Field of the Invention
This invention relates to a method to produce succinic acid, malic acid or fumaric acid, and more particularly this invention relates to a bacteria that produces high quantities of succinic acid, malic acid and fumaric acid.
2. Background of the Invention
Carboxylic acids hold promise as potential precursors for numerous chemicals. For example, succinic acid can serve as a feedstock for such plastic precursors as 1,4-butanediol (BDO), tetrahydrofuran, and gamma-butyrolactone. New products derived from succinic acid are under constant development, with the most notable of these being polyester which is made by linking succinic acid and BDO. Generally, esters of succinic acids have the potential of being new, "green" solvents that can supplant more harmful solvents and serve as precursors for millions of pounds of chemicals annually at a total market value of over $1 billion. Along with succinic acid, other 4-carbon dicarboxylic acids, such as malic acid, and fumaric acid also have feedstock potential.
The production of these carboxylic acids from renewable feedstocks (in this case through fermentation processes) is an avenue to supplant the more energy intensive methods of deriving such acids from nonrenewable sources. Succinate is an intermediate for anaerobic fermentations by propionate-producing bacteria but those processes result in low yields and concentrations.
Anaerobic rumen bacteria, such as Bacteroides ruminicola and Bacteroides amylophilus also produce succinate. However, rumen organisms are characteristically unstable in fermentation processes.
It has long been known that a mixture of acids are produced from E.coli fermentation, as elaborated in Stokes, J. L. 1949 "Fermentation of glucose by suspensions of Escherichia coli" J. Bacteriol. 5 7:147-158. However, for each mole of glucose fermented, only 1.2 moles of formic acid, 0.1-0.2 moles of lactic acid, and 0.3-0.4 moles of succinic acid are produced. As such, efforts to produce carboxylic acids fermentatively have resulted in relatively large amounts of growth substrates, such as glucose, not being converted to desired product.
Some bacteria, such as A. succiniciproducens, utilized in fermentation processes as outlined in U.S. Pat. No. 5,143,834 to Glassner et al., naturally produce succinic acid in moderate yields. However, this host organism converts at most 1 mole of carbohydrate to 1.33 moles of succinate and 0.67 moles of acetate. Production of the acetate co-product illustrates that one-third of the expensive glucose is not converted to succinate. Furthermore, the A. succiniciproducens host strain has been shown to be not highly osmotolerant in that it does not tolerate high concentrations of salts and is further inhibited by moderate concentrations of product. Lastly, A. succiniciproducens presents handling problems in that as an obligate anaerobe, procedures using the organism must be done in the absence of oxygen. Also, medium preparation for the inoculum requires the addition of tryptophan and also requires the mixing of four different solutions, one of which contains corrosive and toxic H.sub.2 S.
A need exists in the art for a fermentation process to economically produce high amounts of carboxylic acids, such as succinic acid, malic acid and fumaric acid. The process should utilize low cost nutrients and substrates yet provide for high fermentation rates. To effect such a process, an osmotolerant, well-characterized facultative bacterial host is required to yield desired product in up to a 2:1 molar ratio of product-to-growth substrate.